The present invention relates to a fuel injection pump for internal combustion engines.
More particularly, it relates to a fuel injection pump which has a pump plunger enclosing a pump work space in a pump cylinder and a cam drive controlling the reciprocating movement of the pump plunger.
In such a known fuel injection pump a non-return valve opening into the suction space of a distributor fuel injection pump is arranged in the fuel duct downstream of the magnet valve in the flow direction toward the fuel tank. In addition, the rear of the non-return valve in the filling duct is connected with the fuel duct. The object of this arrangement is to prevent the non-return valve serving to fill the pump work space from opening in the event that the electrically actuated valve remains stuck in its closed position. This would cause an excess quantity of fuel to be delivered with each delivery stroke of the pump plunger since there exists between the electrically actuated valve and the non-return valve of the fuel duct a counter-pressure which is determined by the opening pressure of the non-return valve in the fuel duct and is greater than the opening pressure acting on the non-return valve in the filling duct. Accordingly, the internal combustion engine is protected from damage as a result of defective operation of the electrically actuated valve.
In other fuel injection pumps it is known to fill and also to empty the pump work space via the electrically actuated valve. In so doing, the electrically actuated valve must be outfitted with a sufficiently large opening cross section so that the injection phase can be terminated quickly and the pump work space can be filled from the fuel tank during its filling stroke at a constant pressure. This large cross section increases the cost of the electrically actuated valve which is preferably constructed as a magnet valve. Moreover, at a given electromagnetic force the actuating time increases with the opening cross section, which works to the disadvantage of an exact and quick control in all speed ranges of the internal combustion engine.